This proposal seeks support for a series of investigations to define the molecular determinants of ion-permeable channels in lipid bilayers. The channel-forming molecules will be L-amino acid peptides of known primary structure and will be designed on the basis of estimates of their hydrophobicity and their hyrophobic moment. These molecules will be tested for their ability to form channels in phospholipid membranes through measurements of the characteristics of the single channel conductance, as a function of voltage and as a function of the ionic composition and concentration of the aqueous environment. The characterization of the interaction of the peptides with bilayers will also include measurements of the macroscopic conductance (multi-channel membranes) to determine its voltage dependence and the peptide- and salt-concentration dependence, in order to obtain estimates of the molecularity of the channel-forming entity as well as an estimate of the gating charge. In this project we propose to work with the following synthetic peptides: a) Three naturally occurring forms of melittin (from different Apis species). b) Apis Mellifera melittin in which Lys-7 (the potential gating charge) will be replaced by amino acids containing non-ionic or ionic (negatively charged or uncharged) polar side chains, as well as by amino acids containing nonpolar aliphatic or aromatic side chains. c) A. Mellifera melittin in which the highly polar C-terminal end will be modified by replacement of the polar amino acids. d) The leader sequence of parathyroid hormone and biologically active, as well as biologically inactive analogues. e) The leader sequence of the atrial natriuretic factor. The results of our experiments on the capacity of selected peptides to form ion-permeable channels will be used to correlate the properties of these channels with their hydrophobicity and hydrophobic moment, to test the hypothesis that channel-forming peptides must have sufficient hydrophobicity to penetrate the hydrophobic interior of the bilayer, must also have a high enough helical hydrophobic moment in order to produce aggregation of the monomers of the peptide and to provide for a hydrophilic lumen to allow passage of ions.